Germany’s oldest party was founded in 1875, and is described as "center-left". It roots in the 19th century labor movement.
The SPD is the second largest party in terms of voter support, but the largest in terms of membership. Its voter base is the working class in urban areas. SPD icon Willy Brandt was foreign minister in the first "grand coalition" government with the CDU 1966-1969 and then became the first SPD chancellor.
Last weekend Chancellor Angela Merkel's Christian Democratic Union Party scored a big win in a key state election. In North Rhine Westphalia, the CDU seized power from the Social Democrats whose chief, Martin Schulz is Merkel's main challenger in the September federal elections. Berlin correspondent is Daniel Pelz explains how significant the state election victory was for the Chancellor.
After its defeat in the North Rhine-Westphalia state election, the center-left SPD has rejected a coalition with Angela Merkel's CDU. The news might be a boon to the resurgent business-friendly FDP - also nationally.
The election result in North Rhine-Westphalia has confirmed the trend on the federal level: Chancellor Angela Merkel is a big step closer to a fourth term. Her SPD opponent Martin Schulz has been considerably weakened.
Winning Germany's most populous state - the last to vote before September's general election - could provide key momentum. And there are many other reasons why parties want a strong showing in North Rhine-Westphalia.